Mediums don't usually crit that hard if you just for a hit phase x2 hit, but if you go phase MLLL you can build up cruelties and your mediums will crit much harder, also before the SP2 I sometimes like to throw a heavy to get a fury or cruelty buff. SP2 hits quite hard regardless of any of those buffs, but with buffs oh boy even without suicides she's a monster
3 or 4K mediums on a maxed 5* ghost is pretty normal. I felt the same when I first rank 5ed my ghost. Her cruelty, sp2s, and the general utility of phasing completely makes up for it.
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Also like mentioned above, throw a heavy or two right before the sp2 to stack some furies and go crazy
https://www.youtube.com/channel/UC4hyP-GvRHzfsT-Gdd63_ZA
She usually hits in the mid 20K range on a sp2.
My 6* hits considerably harder